Add a ".gitlab-ci.yml" to the module, to ensure its stability

We should try this carefully. Let's say it's minor.

Hello @Grevil
Added the MR for providing a sample for Add a ".gitlab-ci.yml" to the module, to ensure its stability.
Kindly review the changes.

Thank you.

Hello @Shreya_th, thanks for your work, but I think we should align the yml to the officially maintained yml found here: https://git.drupalcode.org/project/gitlab_templates/-/blob/1.0.x/gitlab-....

But as Drupal seems to be in the midst of replacing Drupal CI with Gitlab CI, we should just postpone this issue and wait for it to be officially added.